The present invention relates to a semiconductor memory device, and more particularly, to a semiconductor memory input/output device supporting a multi-operation mode.
In order to increase an operating speed of a semiconductor memory device, recent semiconductor technology continuously increases an operating frequency. Additionally, the number of data bits simultaneously inputted to or outputted from the semiconductor memory device increases. As a result, recent semiconductor memory devices include an increased number of pads for inputting and outputting data.
For example, a semiconductor memory device supporting an X8 operation mode includes eight data pads for inputting and outputting 8-bit data at the same time, two data strobe pads for a data strobe signal, a selection pad for a data mask signal or a read data strobe signal, and an inverted read data strobe pad for an inverted read data strobe signal.
Referring to FIG. 1, the conventional semiconductor memory device supporting an X8 operation mode includes a selection pad 1 and an inverted read data strobe pad 2. The selection pad 1 is controlled by a first setting signal RDQSEN that is generated by a set value of an extended mode register set EMRS. The selection pad 1 outputs a read data mask signal RDQS outputted from an output buffer 3 or transfers a data mask signal DM from an external device to an input buffer 4.
The inverted read data strobe pad 2 is controlled by a second setting signal RDQSbEN that is generated based on a set value of an extended mode register set EMRS and outputs an inverted read data mask signal RDQSb from an output buffer 5.
Here, the set value of the extended mode register set EMRS is decided based on an extended mode register set EMRS and address fields A11 and A10 when a semiconductor memory device operates in an X8 operation mode defined in DDR2 SDRAM specification.
According to the DDR2 SDRAM specification, if a value of the address field A11 that sets an extended mode register set is logic high, a read data strobe signal RDQS is used and a data mask signal is not used in the X8 operation mode. Accordingly, when the semiconductor memory device operates in the X8 operation mode, it is possible to share one pad for both of the lower data mask signal LDM and the read data strobe signal RDQS because the lower data mask signal LDM and the read data strobe signal RDQS are exclusively used in the X8 operation mode.
According to the DDR2 SDRAM specification, if a value of the address field A10 setting an extended mode register set EMRS is logic ‘low’, an inverted read data strobe signal RDQSB is used and an inverted data strobe signal DQSB is not used. Accordingly, the inverted read data pad outputs the inverted read data strobe signal RDQSB.
Meanwhile, the semiconductor memory device is designed to support a multi-operation mode for expanding generality. The multi-operation mode enables to select more than two of operation modes. For example, a semiconductor memory device is designed to enable a user to select one of an X16 operating mode and an X8 operation mode.
According to a related art, a semiconductor memory device supporting the X16 operation mode and the X8 operating mode includes 16 data pads and 4 data strobe pads.
When a semiconductor memory device operates in the X16 operation mode, the semiconductor memory device inputs or outputs 16-bit data through 8 upper data pads UDQ0 to UDQ7 and 8 lower data pads LDQ0 to LDQ7 and inputs or outputs upper and lower data strobe signals UDQS, UDQSb, LDQS and LDQSb through 2 upper data strobe pads and 2 lower data strobe pads that strobe upper and lower data inputted or outputted through the upper and lower data pads UDQ0 to UDQ7 and LDQ0 to LDQ7.
When a semiconductor memory device operates in the X8 operation mode, the semiconductor memory device inputs or outputs 8-bit data through 8 lower data pads LDQ0 to LDQ7 and inputs or outputs lower data strobe signals LDQS and LDQSb through two lower data strobe pads.
As shown in FIG. 2, the semiconductor memory device supporting the X16 operation mode or the X8 operation mode further includes a data mask pad, an inverted read data mask pad, and a selection pad.
In the X16 operation mode, the selection pad 21 and the data mask pad 23 transfer lower and upper data mask signals LDM and UDM to the input buffers 25 and 27. Here, the lower and upper data mask signals LDM and UDM are inputted for masking lower and upper data from an external device.
In the X8 operation mode, the selection pad 21 transfers a lower data mask signal LDM inputted from an external device by a first setting signal RDQSEN to an input buffer 25 or outputs a read data strobe signal RDQS outputted from the output buffer 24. The inverted read data strobe pad 22 outputs the inverted read data strobe signal RDQSb which is selectively outputted from the output buffer 26 by the second setting signal RDQSbEN that is controlled by a set value of an extended mode register set EMRS.
As described above, the conventional semiconductor memory device supporting a multi-operation mode includes an upper data mask pad for the X16 operation mode, which is not used for the X8 operation mode and also includes the inverted read data strobe pad for the X8 operation mode, which is not used for the X16 operation mode.
As a result, an overall size of a semiconductor memory device increases because the semiconductor memory device includes more pads for supporting the multi-operation mode. Since lines and pads must not be overlapped, it becomes very difficult to dispose lines in a semiconductor memory device if the number of pads increases. The operation characteristics of the semiconductor memory device are deteriorated.